The present invention relates to a method of assembling an intake manifold to an internal combustion engine having two cylinder banks. More particularly, it relates to a method of fastening the intake manifold to cylinder heads while using a technique for reducing each deformation of cylinder bores formed in the cylinder heads of the internal combustion engine.
Hitherto, as for the mounting of one or more cylinder heads on a cylinder head of the internal combustion engine, a problem of piston slap noise has been caused during the engine's operation since the cylinder bores is deformed by a fastening force (an axial force) applied on cylinder head bolts for fastening the cylinder head. Note, the cylinder head bolts will be also referred to as "head bolts", hereinafter.
In order to reduce such a deformation of the cylinder bores, for example, rib or bridge structures for reinforcing the cylinder block are disclosed in Japanese Unexamined Patent Publications (kokai) Nos. 58-13256 and 6-346782.
However, it is coming to light that, in the internal combustion engine where the intake manifold is interposed between a left cylinder bank and a right cylinder bank, such as in a V-type engine having two cylinder banks arranged in a substantial V form, the deformation of the cylinder bores is caused by not only the fastening force applied to the head bolts but another fastening force applied to bolts used to mount the intake manifold to the cylinder heads.
It should be noted that, due to variations in machining accuracy and assembling accuracy of the cylinder heads etc., respective fitting surfaces of the intake manifold and the cylinder heads in the V-type engine are not always parallel with each other. Thus, in the conventional fastening method of the intake manifold, the intake manifold has been displaced by making use of the fastening force exerted on the bolts for fastening the intake manifold to the cylinder heads, thereby adhering the fitting surfaces to each other in order to ensure the sealing performance therebetween. Consequently, as shown in FIG. 1, an action line of a force F of an intake manifold 1, due to the urging of a cylinder head 2 when assembling the intake manifold 1, is out of alignment with another action line of a frictional force f (reaction force of F) of the cylinder head 2, so that a rotational moment (couple of forces) M is produced that is exerted on the cylinder head 2. Further, since an outer wall of a cylinder block 3 is urged outward, together with the moving cylinder head 2 by the rotational moment M, cylinder bores are deformed in a thrust direction (see FIGS. 2A and 2B). Additionally, not only is the fastening force providing the surface pressure for ensuring the sealing performance of the fitting surfaces, but also the fastening force for displacing the cylinder head 2 is applied on an intake manifold bolt 4 for fastening the intake manifold 1 to the cylinder head 2. Consequently, such an application of the fastening forces on the intake manifold bolt 4 causes female threaded portions in bolt-holes formed on the cylinder head 2 to be further deformed, thereby increasing the deformation of the cylinder bores.
In order to reduce such a deformation of the cylinder bores, it is suggested to further reinforce the cylinder block by means of ribs or the like. Such reinforcement, however, would cause the weight of the cylinder block to be increased and would require modification of the present design of the cylinder block.